In recent years, in-vivo functions of nucleic acids are much interested. Particularly, there are many cases where an RNA controls expression of a gene. In view of this, there is a prospect that development of drugs targeting RNAs will be sped up.
Generally, development of a drug starts from first screening. In the first screening, a library of candidate substances, which are candidates for the drug, is screened so that a substance bindable to a substance targeted by the drug is specified. Here, how quickly the first screening is performed is important, because this determines the development speed of the drug. For example, in a case where a target of a drug is an RNA, such a method is required that easily and quickly examines a binding affinity between the RNA and candidate substances so that a screening is quickly performed to specify a candidate substance bindable to the RNA.
Conventionally used method for examining a binding affinity between a nucleic acid such as an RNA and a candidate substance is as follows: The nucleic acid is immobilized to a detecting device such as a bead, or is caused to bind to a fluorescent dye, and then a signal changing due to an interaction therebetween is detected. For example, Non-Patent Literature 1 discloses a displacement assay by which a binding affinity between Rev protein and RRE (Rev Protein Responsible Element) in mRNA of an AIDS virus HIV-1 is measured based on whether or not Rev protein substitutes ethidium bromide which has bound to RRE. Ethidium bromide binding to a double strand nucleic acid emits fluorescence in response to irradiation of excitation light thereon. If Rev protein binds to RRE in place of ethidium bromide which has bound to RRE, ethidium bromide is liberated from RRE. This reduces fluorescence detected. Based on this reduction in fluorescence, the binding affinity between RRE and Rev protein is measured. A substance bindable to RRE is disclosed also in Non-Patent Literature 2.
As to binding between DNAs, Patent Literatures 1 to 3 disclose methods in which a DNA labeled with a xanthone fluorescent dye is used as a primer and is annealed to a target DNA fragment. Details of xanthone are disclosed in Patent Literatures 4 to 6 and Non-Patent Literature 3.
Patent Literature 1
Japanese Unexamined Patent Publication, Tokukaihei, No. 9-124636 A (Publication Date: May 13, 1997)
Patent Literature 2
Japanese Unexamined Patent Publication, Tokukai, No. 2004-225049 A (Publication Date: Aug. 12, 2004)
Patent Literature 3
Japanese Unexamined Patent Application Publication (Translation of PCT Application), Tokuhyo, No. 2004-532805 A (Publication Date: Oct. 28, 2004)
Patent Literature 4
Japanese Unexamined Patent Publication, Tokukaihei, No. 10-101591 A (Publication Date: Apr. 21, 1998)
Patent Literature 5
Specification of U.S. Patent Application Publication No. 2005/0171079 (Publication Date: Aug. 4, 2005)
Patent Literature 6
Specification of U.S. Patent Application Publication No. 2005/0234031 (Publication Date: Oct. 20, 2005)
Non-Patent Literature 1
Nathan W. Luedtke, Yitzhak Tor, Fluorescence-based methods for evaluating the RNA affinity and specificity of HIV-1 Rev-RRE inhibitors, Biopolymers, Vol. 70, Issue 1, p. 103-119.
Non-Patent Literature 2
Nihon Kagaku Kai, Dai 83 Kai, Shunki Taikai, Koen Yokoshu (Abstracts, The 83rd Annual Meeting of The Chemical Society of Japan), Mar. 3, 2003, page 1102, 1G8-37
Non-Patent Literature 3
IUPAC Name: 2,7-bis(2-aminoethoxy)xanthen-9-one, [online], NCBI PubChem, CID: 11659655, Create Date: 2006-10-27, [Searched on Jul. 13, 2007] The Internet <URL: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?ci d=11659655>